Designs of light air-cushion vehicles with a single propulsion unit wherein a part of the airflow from the pulling or pushing fan is directed in a cavity of the air chamber in the bottom creating conditions for the vehicle hovering are presently known in the art (for example, patents U.S. Pat. No. 3,869,020, B60V 1/14 , 1975 (1), U.S. Pat. No. 5,007,495, B60V 1/14, 1991 (2), U.S. Pat. No. 3,608,663, B60V 1/14, 1971 (3)).
The vehicles with entire airflow from a propelling fan directed in the air cushion chamber are also known (patents U.S. Pat. No. 3,669,212, B60V 1/14, 1972 (4) and U.S. Pat. No. 3,401,766, B60V 1/00, 1965 (5)). At the same time part of the flow can be directed to any side by opening valves of a corresponding side providing rather free maneuvering. “Pulling” power of such vehicles is not big since the pressure in the cushion can not exceed the pressure required for hovering, and when the pressure grows it is released unevenly at all sides. Taking into account that a thrust always exists due to air “sucking in”, it is neutral only in case the fan is in horizontal position. When the fan is inclined ahead, the apparatus starts moving in the direction of fan inclination even if the air outflows uniformly along the whole perimeter of the air cushion.
The fan thrust practically can not be balanced with releasing air from the air cushion cavity in the direction providing back thrust, i.e., in reverse (under physics laws), as suggested in (5), though it is possible to control motion and decrease the “direct” thrust down to almost zero.
The motion control in (4) with rudders arranged behind the fan is due to eccentricity of the thrust in relation to the longitudinal axis of the apparatus, and the effectiveness of the control as well as the entire propulsion complex is extremely low.
A technical solution according to reference (3) is known, wherein the control surfaces are placed directly behind the fan in the propulsion duct at the front of the apparatus, and there are rudders at its stem. In usual conditions the apparatus has good characteristics of controllability at cruising regime and acceleration mode.
Direct thrust can be almost zero if the thrust duct is completely closed with flaps at the output of the duct; however in such case the control over the apparatus is lost.
Another design of a light air-cushion vehicle is known from (2). In this case control of motion direction is provided by a single multilink bucket reversing device. This solution is also characterized by complete absence of clarity how to control the apparatus in the mode of “reverse”. What is more, control characteristics of the apparatus can be so nonlinear that it would be technically impossible to control apparatus motion.
The coefficient of the back thrust of the reversing devices is well investigated in aviation. It is not more than 0.4 even in case of thorough engineering (it is 0.35 for NK-8-2U engine of TU-154 airplane). It can even be zero in “short” apparatus like the one described in (2). An attempt of complex solution of controlling and reversing problems is in source (1). Here there is theoretical possibility to control the direction of motion at complete thrust reversing in reversing flap position shown in FIG. 13 due to release of flaps “142” and “146” though release of the control flaps decreases back thrust and possibly leads to a side force at the apparatus body contrary to the desired result due to the effect of aerodynamic “curvature” of the apparatus erection profile. It is especially dangerous at high speed as the relation is nonlinear.
The review of the known designs of air cushion apparatuses shows the following:
1. None of the designs solves the problem of apparatus thrust control satisfactorily (from maximum positive to maximum in reverse direction).
2. None of the designs offers a solution of the problem of quality apparatus position control in braking mode at high speed.
3. None of the solutions is suitable for position and motion direction control at zero or close to zero speed, at the same time providing satisfactory thrust and propulsive efficiency of the moving device.